This is a more complex method to configure the chart than chartData but offers a lot more possibilities.
See a List of properties, you can set per line, or bar:
[{"data":"OverallPrice",//the column to take for the line values from the sub dataset"color":"red",//line color"fill":"false"//do not fill the gap to the bottom line},{"data":"OwnPrice",//the column to take for the line values from the sub dataset"color":"blue","backgroundColor":"yellow",//background color for the gap or the bar, in case of a bar chart"fill":"0"//means you fill the gab to the first (0) line. }]